1. Field of the Invention
The present invention relates to an alignment and exposure process. More particularly, the present invention relates to an alignment and exposure process that use the same light source.
2. Description of the Related Art
Typically, the photolithography process is an important part of the semiconductor process. The photolithography process comprises the steps of forming a photoresist over a substrate. A light from a light source is projected onto the photoresist through a mask to replicate a pattern on a mask in the photoresist. After the developer process and the etching process are performed, the photoresist is removed. Therefore, the pattern on the mask is completely replicated in the target dielectric layer on the substrate.
In the photolithography process, before the pattern is formed in the target dielectric layer, it is important to align the mask with the wafer. Every pattern alignment process is an accurate alignment process. In order to accurately align the mask with the wafer, there are some marks, which are alignment marks, on the predetermined location. These marks are used as alignment standards during the alignment process.
Since the accuracy of the semiconductor process is increasingly critical as the integration of the integrated circuit rises, even a tiny error occurring in the process may lead to the failure of the process. Hence, wafer consumption and the cost are increased.
Currently, the light sources used in the alignment process and the exposure process are different. A red-light source is used to perform the alignment process. A blue-light source such as ultraviolet rays or deep ultraviolet rays is used to perform the exposure process. However, after the red-light alignment process and the blue-light exposure process, what is known as a red-blue shift occurs due to the wavelength difference. In order to decrease the misalignment probability, it is necessary to compensate for the red-blue shift by extra equipment calibration.